1. Field of the Invention
The present invention relates to a thermostat valve and, more particularly, a thermostat valve of the type which utilizes the reversable expansion and contraction of a thermally expandable material such as wax for operating a valve member between its open and closed positions.
2. Description of the Prior Art
As a thermostat valve of the aforementioned type, there is known a thermostat valve comprising a housing having a valve seat portion which defines a valve port, a valve member adapted to cooperate with said valve seat portion to selectively open or close said valve port, a casing member containing a thermally expandable material such as wax and providing a cylindrical bore, and a needle partially received in said bore so as to be slidable therealong and driven by said thermally expandable material relative to said casing member due to the thermal expansion of said material, wherein either said casing member or said needle is connected to said housing while the other is connected to said valve member.
The thermostat valve of this type is mounted, for example, at the cooling water outlet port of a water jacket of the automobile engine for the purpose of controlling the cooling water temperature in its water cooling system. In this case, when the cooling water temperature is low, the valve is closed to close the cooling water outlet port of the water jacket thereby obstructing the flow of cooling water from the water jacket toward the radiator while, when the cooling water temperature increases, the valve is opened to open the cooling water outlet port thereby allowing the cooling water to flow from the water jacket toward the radiator.
In the conventional thermostat valve of the abovementioned type, the needle is formed as a straight rod member having a uniform cross section, said rod member being relatively, closely received in said bore without leaving any substantial clearance between the sliding surfaces of the two relative slidable members. In this case, when the valve has been used for a long time, the friction shavings generated from a rubber piston, a resin plate, etc., provided in said bore, the fur in the cooling water, etc., accumulate between the needle and the bore thereby increasing the slide resistance of the needle and causing misoperation so that even when the thermally expandable material is contracted, the needle is not retracted thereby keeping the valve in its opened condition. If such a misoperation occurs in a thermostat valve provided in the engine cooling system of an automobile, the cooling water temperature is not properly maintained in the winter season, causing overcooling of the cooling water, whereby the startability of the engine and the fuel consumption become poor and the sufficient heating of the cabin is obstructed.
Furthermore, if a portion of the thermally expandable material leaks out of the casing member as a result of an overexpansion thereof due to overheating caused by an extrordinarily high temperature of the engine cooling water caused by some problem in the engine, then the valve will not be sufficiently opened in a subsequent normal operation, whereby chronic overheating of the engine will occur and, in an extreme case, very serious damage such as burn sticking of the engine will be caused.